Using satellite‐derived estimates of plant phenological rhythms to predict sage‐grouse nesting chronology

Abstract

The “green wave” hypothesis posits that during spring consumers track spatial gradients in emergent vegetation and associated foraging opportunities. This idea has largely been invoked to explain animal migration patterns, yet the general phenomenon underlies trends in vertebrate reproductive chronology as well. We evaluated the utility of this hypothesis for predicting spatial variation in nest initiation of greater sage‐grouse ( Centrocerus urophasianus ), a species of conservation concern in western North America. We used the Normalized Difference Vegetation Index (NDVI) to map the green wave across elevation and then compiled dates and locations of >450 sage‐grouse nests from 20 study sites (2000–2014) to model nest initiation as a function of the start of the growing season (SOS), defined here as the maximum daily rate of increase in NDVI. Individual sites were drawn from three ecoregions, distributed over 4.5° latitude, and spanning 2,300 m in elevation, which captured the climatic, edaphic, and floristic diversity of sagebrush ecosystems in the southern half of current sage‐grouse range. As predicted, SOS displayed a significant, positive relationship with elevation, occurring 1.3 days later for each 100 m increase in elevation. In turn, sage‐grouse nest initiation followed SOS by 22 ± 10 days ( r 2 = .57), with hatch dates falling on or just prior to the peak of the growing season. By timing nesting to the green wave, sage‐grouse chicks hatched when the abundance of protein‐rich invertebrate biomass is hypothesized to be nearing a seasonal high. This adaptation likely represents a strategy for maximizing reproductive success in the arid, variable environments that define sagebrush ecosystems. Given projected changes in climate and land use, these results can be used to predict periods of relative sensitivity to habitat disturbance for sage‐grouse. Moreover, the near real‐time availability of satellite imagery offers a heretofore underutilized means of mapping the green wave, planning habitat restoration, and monitoring range conditions.

Greater sage-grouse face tradeoffs between predation risk and thermal exposure in selecting habitat

“…In Spring and Autumn, when thermal extremes were less common, sage-grouse in Buckskin showed less selection for areas near trees than during the higher maximum temperature in Summer. While metrics of vegetation cover and activity such as Normalized Difference Vegetation Index (NDVI) are important for sage-grouse (Dinkins et al 2017, Stoner et al 2020, the grouse in this study generally selected areas with moderate temperatures and avoided extremes where possible, suggesting that temperature also drives selection. In Steptoe and Buckskin, most of the mesic habitat, which sage-grouse tend to select during late brood rearing (summer), is not treed riparian areas like in some areas of sage-grouse distribution, and there is likely little direct correlation between tree cover and mesic resources.…”

Resource allocation effects on the timing of reproduction in an avian habitat specialist

“…2009, Stoner et al. 2020). Sage‐grouse females tend to be philopatric to their nest sites, so females that first nest at high elevations continue to do so through their life.…”

“…Biologically important elevational gradients that occur over small spatial scales create heterogeneity in vegetation phenology (Crimmins et al 2010), which promotes an evolved response to environmental variation in life-history strategies of animals (Bears et al 2009, Stoner et al 2020. Sage-grouse females tend to be philopatric to their nest sites, so females that first nest at high elevations continue to do so through their life.…”

Is the grass always greener? Land surface phenology reveals differences in peak and season‐long vegetation productivity responses to climate and management

“…Vegetation phenology interacts with climate and has cascading impacts to ecosystem processes such as nutrient cycling and the maintenance of ecosystem services (Beard et al., 2019 ; Cleland et al., 2007 ; Morisette et al., 2009 ). Furthermore, wildlife species within a system may respond to vegetation phenology and productivity with potential cascading effects on seasonal timings, fecundity, interspecific interactions, and behavior (Donnelly et al., 2018 ; Rehnus et al., 2020 ; Stoner et al., 2020 ).…”